I've currently got the same thing - my left nipple is tender, and somewhat swollen, with a little red dot, where an opening is. I stay in a lot o hotels and sweat a lot at night. It might be hard sleeping drenched in sweat. Either way, I've just now put neosporin on it, and might get it checked if it does not go away. The other nipple seems fine. I'm 35 and eat well, exercise but drink beer daily. Just not sure what it is.
Hi.
From your description, it seems that your male friend has an infection in the area of the nipple that caused the pain and swelling. Organisms can be introduced when there are breaks in the skin. These organisms can proliferate and result in inflammation.
You should have it checked by his doctor. Appropriate antibiotic should be started. Pain relievers can also help.
Take care.